Oxidation of naphthenic acids to polybasic acids



United States Patent OXIDATION OF NAPHTHENIC ACIDS TO POLYBASIC ACIDS Norman W. Franke, Penn Township, Allegheny County, Pa., and Peter B. Kelly, College Station, Tex., assignors to Gulf Research & Development Company, Pittsburgh, Pa., a corporation of Delaware No Drawing. Application September 15, 1955 Serial No. 534,621

6 Claims. (Cl. 260-537) We have found that dibasic carboxylic acids can be I obtained in a relatively simple manner by oxidizing naphthenic acids in the presence of a strong oxidant.

Naphthenic acids which can be employed as charge stock in the present application can be defined as cycloparafiinic compounds containing at least one carboxylic acid group per molecule, particularly those whose boiling points range from about 390 to about 660 F. and whose molecular weights vary from about 128 to about 480. As charge stock for the process of this invention any of the naphthenic acids defined above or mixtures of such naphthenic acids can be employed. Preferably the charge stock consists almost solely of naphthenic acids, although minor amounts of other compounds or materials which do not adversely affect the course of the oxidation reaction or reaction or react with the reactant, oxidant or product obtained can also be present. Included among the naphthenic acids which are suitable as charge stock in the present invention are methylcyclopentane carboxylic acid, dimethylcyclopentane carboxylic acid, methylcyclohexyl carboxylic acid, methylcyclohexyl acetic acid, etc.

We have found that the oxidizing action necessary to produce appreciable yields of dibasic carboxylic acids must be strong and therefore mere air blowing will not suffice, although an oxygen-containng gas such as air in combination with a strong oxidant can be employed to reduce the consumption of said strong oxidant for the amount of product obtained. In such case we prefer to employ up to about 100 percent by weight of molecular oxygen based upon the strong oxidant employed. While under the reaction conditions hereinafter set forth any strong oxidant can be employed to obtain appreciable yields of dibasic carboxylic acids, exceedingly good results are obtained with nitric acid. Other strong oxidants, such as chromic acid, alkali metal permanganates, for example potassium permanganate, etc., can also be employed. In carrying out the process of the present invention We can employ a single oxidant or a combination of strong oxidants. The oxidation process can be conducted with or without the aid of an oxidation-promoting catalyst. Included among the oxidation-promoting catalysts suitable in the process are ammonium metavanadate, potassium permanganate and cobalt nitrate.

The ratio of oxidant to naphthenic acids is not critical, although an amount of oxidant in excess of that theoretically required to oxidize the naphthenic acids in the charge to dibasic carboxylic acids is recommended. In general a ratio of at least about two parts, and preferably at least about four parts, of oxidant per part of naphthenic acids is satisfactory.

The concentration of the oxidant employed in the oxidation process is not critical, although it should be high enough to convert a substantial amount of the naphthenic acids to dibasic carboxylic acids in a reasonable length of time. Thus, the concentration of the nitric acid can be as low as about 30 percent or as high as about percent, although a concentration of about 70 percent is generally preferred. In the case of oxidants such as chromic acid and potassium permanganates, for example, approximately stoichiornetric amounts of the oxidants at very low concentrations are satisfactory.

The oxidation reaction of this invention can be carried out over a wide range of temperatures. Thus temperatures as low as about 70 C., or lower, can be employed and a satisfactory reaction will take place. Since it is desirable, from an economic viewpoint, but not absolutely necessary, to carry out the reaction in the liquid phase, the upper temperature at atmospheric pressure is about C. While it is preferred to carry out the reaction at atmospheric pressure, the reaction can also be carried out at elevated pressures as high as about 1000 pounds per square inch gauge. As the pressure is raised the temperature can correspondingly be raised from about 100 to about C.

The time required for the substantial completion of the reaction will depend of course upon the selection of variables defined hereinabove. Since the present reaction is exothermic, from a practical point of view the time required will depend, to a large part, upon the rate at which heat produced can be removed from the reaction system. A period of at least about /2 hour and preferably about one to about 100 hours is generally satisfactory to convert the naphthenic acids to the corresponding dibasic car boxylic acids.

The process of this invention can best be illustrated by the following examples.

Example I A solution of 0.1 gram ammonium metavanadate in 400 ml. of 70 percent nitric acid was stirred with 100 grams of petroleum naphthenic acids (having a boiling range of about 50 to about C. at 2 mm. Hg) and heated to 85 C. and maintained at the latter temperature for 96 hours to obtain a product comprising a hydrocarbon layer and an aqueous layer. The two layers were separated and the aqueous layer was then evaporated under aspirator vacuum. A series of there additions of 250 ml. of water followed by evaporation was run. The product was then dissolved in acetone, filtered to remove the vanadate and reevaporated. The yield of product was 52 percent. The product obtained was analyzed and the neutralization number was found to be 645, the molecular weight 188. This corresponds to a dibasic carboxylic acid having the formula C H (COOH) As a further check, the product was esterified with n-butanol and an analysis of a cut boiling between 125 and C. at 2.5 mm. Hg was found to have a molecular weight of 246 and a saponification number of 402. This compares with a calculated molecular weight of 284 and a calculated saponification number of 394.

Example [I 400 grams of petroleum naphthenic acids having a boiling range of about 100 to about 125 C. at 2.5 mm. Hg was oxidized as in Example I using 1600 grams of 70 percent nitric acid containing one gram of ammonium vanadate. The product consisted of two layers which were separated by decantation. The lower aqueous layer was evaporated under vacuum and three one-liter portions of water were added and evaporated to remove the last traces of nitric acid. The yield of acids from the lower layer was 55 percent. The product otbained was then esterified with 2-ethylhexanol and passed through a column of fullers earth. A cut boiling at 175 to 250 C. at 5 mm. Hg was analyzed and found to have a saponification number of 325 and a viscosity at 100 and 210 F. of 20.8 and 3.89 centistokes, respectively. This compares with a calculated saponification number of 346 for the ester obtained by reacting a dibasic carboxylic acid having the formula C H (COOH) and 2-ethylhexanol. An ultimate analysis of the ester was made with the following results: 69.50 percent carbon, 10.64 percent hydrogen and 19.86 percent oxygen. The calculated analysis of an ester having the formula is as follows: 72.29 percent carbon, 11.64 percent hydrogen and 16.07 percent oxygen.

Obviously many modifications and variations of the invention, as hereinabove set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for producing dibasic carboxylic acids which comprises oxidizing a naphthenic acid whose boiling point ranges from about 390 to about 660 F. and whose molecular weight resides within the range of about 128 to about 480 in the presence of a strong oxidant selected from the group consisting of nitric acid, chromic acid and alkali metal permanganates at a temperature of about 70 to about 150 C. and a pressure of about atmospheric to about 1000 pounds per square inch gauge for a period of about one-half to about 100 hours.

2. A process for producing dibasic carboxylic acids which comprises oxidizing a naphthenic acid whose boiling point ranges from about 390 to about 660 F. and whose molecular weight resides within the range of about 128 to about 480 in the presence of nitric acid at a temperature of about 70 to about 150 C. and a pressure of about atmospheric to about 1000 pounds per square inch gauge for a period of about one-half to about 100 hours.

3. A process for producing dibasic carboxylic acids which comprises oxidizing a naphthenic acid whose boiling point ranges from about 390 to about 660 F. and whose molecular weight resides within the range of about 128 to about 480 in the presence of nitric acid and an oxidation-promoting catalyst at a temperature of about 7 to about 150 C. and a pressure of about atmospheric to about 1000 pounds per square inch gauge for a period of about one-half to about 100 hours.

4. A process for producing dibasic carboxylic acids which comprises oxidizing a naphthenic acid whose boiling point ranges from about 390 to about 660 F. and whose molecular weight resides within the range of about 128 to about 480 in the presence of nitric acid and an oxygen-containing gas at a temperature of about to about 150 C. and a pressure of about atmospheric to about 1000 pounds per square inch gauge for a period of about one-half to about hours.

5. A process for producing dibasic carboxylic acids which comprises oxidizing a naphthenic acid whose boiling point ranges from about 390 to about 660 F. and whose molecular weight resides within the range of about 128 to about 480 in the presence of nitric acid, an oxidation-promoting catalyst and an oxygen-containing gas at a temperature of about 70 to about C. and a pressure of about atmospheric to about 1000 pounds per square inch gauge for a period of about one-half to about 100 hours.

6. A process for producing dibasic carboxylic acids which comprises oxidizing petroleum naphthenic acids having a boiling range of 50 to C. at about 2 mm. of Hg in the presence of nitric acid having a concentration of 70 percent and ammonium metavanadate at a temperature of about 85 C. for a period of about 96 hours.

References Cited in the file of this patent UNITED STATES PATENTS 2,452,741 Fleming Nov. 2, 1948 2,454,047 De V. Finch et al Nov. 16, 1948 2,662,908 Logan Dec. 15, 1953 2,725,396 Winkler Nov. 29, 1955 OTHER REFERENCES Naphthali: Chemie, Technologie und Analyse der Naphthenstiuren, 1927, pp. 39, 42, 43, 87.

Werber et al.: J. Amer. Chem. Soc., vol. 74, pp. 5325 (1952).

KARL 3L, AXLINE.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PatnfNo, 2,890,247 I June 9, 1959 Norman W, Franke t a1 appears. in the printed specification correction and that the said Letters It is hereby oortifie'd error of "tho above patent requiring Patent should Tomi corrootod belowo Columnl, lino 37, atrike out "or reaction"; line 46, for "oxygen-=-' oontaizmg" reafi m oxygen-wonfiaining mm column 2, line 46, for "there" Signed anfi seal-ed this 13th day of October 1959 j (SEAL;

ROBERT C. WATSON Attesting' Officer Com-nissioner of Patenfi 

1. A PROCESS FOR PRODUCING DIBASIC CARBOXYLIC ACIDS WHICH COMPRISES OXIDIZING A NAPHTHENIC ACID WHOSE BOILING POINT RANGES FROM ABOUT 390* TO ABOUT 660* F. AND WHOSE MOLECULAR WEIGHT RESIDES WITHIN THE RANGE OF ABOUT 128 TO ABOUT 480 IN THE PRESENCE OF A STRONG OXIDANT SELECTED FROM THE GROUP CONSISTING OF NITRIC ACID, CHROMIC ACID AND ALKALI METAL PERMANGANATES AT A TEMPERATURE OF ABOUT 70* TO ABOUT 150* C. AND A PRESSURE OF ABOUT ATMOSPHERIC TO ABOUT 1000 POUNDS PER SQUARE INCH GAUGE FOR A PERIOD OF ABOUT ONE-HALF TO ABOUT 100 HOURS. 